Re: Problem with many (160 - 170) sessions in the database on NT

http://www.oreview.com/9805harr.htm

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On NT, the Oracle instance is implemented as a single NT process. This process includes threads that implement each of the tasks required for the instance. Therefore, there is a thread for each of the background and server tasks plus a two-thread overhead. Because each thread shares the same memory space, there is no need to implement the SGA in shared memory; if you implement the SGA within the instance's process memory, it is available to all threads within the process. Oracle's architecture on NT suits the NT process/thread model. However, the single process model restricts the total memory available to threads belonging to the Oracle instance. Prior to NT version 3.51, the memory limit for a single process was only 256MB--a severe limitation for even moderately sized Oracle instances. In NT version 4.0, a process may address up to 4GB of virtual memory. However, 2GB of this memory is reserved for system overhead, allowing only 2GB for Oracle.

At first glance, 2GB might sound like a generous memory allocation for an Oracle instance. But remember that this area of memory must be sufficient to store the SGA and data segments for all Oracle sessions. Furthermore, the 2GB is a virtual memory limit; it's possible that 2GB of virtual memory will be expended when physical memory usage is actually far lower. There are currently two options for extending the 2GB limit: In Windows NT Server Enterprise Edition, you can reduce the system component of process memory to 1GB, allowing up to 3GB of memory for the Oracle instance. On Alpha NT platforms, the very large memory (VLM) option allows up to 8GB of memory to be made available to the Oracle instance. Oracle's multithreaded server option allows multiple client processes to share a smaller number of Oracle server processes. This approach can reduce memory requirements and process overhead. Multithreaded server is also available on NT, but only from Oracle8 onward. Using multithreaded server under Windows NT can reduce the number of threads in the Oracle process as well as overall memory requirements. You may also be able to use the Oracle8 connection pooling and concentrating facilities to further reduce thread and memory overhead. With the release of Windows NT version 5.0 (expected in the fourth quarter of 1998), the process memory limit will increase to 32GB, which should be sufficient for most Oracle installations.

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other stuff that may, or may not, contain helpful info:

http://www.ipass.net/~davesisk/oont.htm
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http://www.geocities.com/tbcox23/
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On 29 May 2001, at 8:50, Jonas A Wetterberg wrote:

Date sent:              Tue, 29 May 2001 08:50:25 -0800
To:                     Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>

>
> We are running into a little problem with an Oracle installation. The server
> OS is Windows NT, SP6, and the version of Oracle is 7.3.4.5.0. The server
> have 4 processes, we have about 1,7 G primary memory and about 2 G of memory
> on swap disk. We have 4 processes in the machine. One of these is reserved
> for the OS, and Oracle uses the other 3.

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